Machining limit area specifying method and manuel feed machining method using numerical control unit

ABSTRACT

A machining limit area specifying method and a manual feed machining method using a numerical control unit capable of easily performing machining in a desired shape by manual feed. In specifying a machining limit area on an X-Y plane, a desired machining shape is defined by shaping data or a combination of some shaping data on the X-Y plane at a predetermined Z-coordinate, and the desired machining shape defined by the shaping data is specified as a machining limit area in which movement of a tool is permitted on the X-Y plane in manual machining using the numerical control unit. In specifying a machining limit area in the Z-axis direction, an inverse function using an X- or Y-coordinate value as a parameter is obtained based on a function for specifying the machining limit area on the X-Y plane on condition that a Z-coordinate value is used as a parameter, and the machining limit area in the Z-axis direction is specified based on the inverse function.

FIELD OF THE INVENTION

The present invention relates to a method of specifying a machininglimit area in which movement of a tool is permitted in manual feed usinga numerical control unit, and to a manual feed machining method usingthe machining limit area.

BACKGROUND OF THE INVENTION

In a numerical control unit for controlling a machine tool such as ageneral-purpose milling machine and a lathe to perform machining, anautomatic operation mode for controlling the machine tool by executing amachining program and a manual feed mode for feeding a tool by manualoperation can be selected. In the manual feed mode, it is possible toperform a manual-continuous feed to continuously drive a machine tool bymanual operation through jog feed or the like, a fine adjustment feedfor driving the machine tool by operating a manual pulse generator, oran increment feed for moving a tool by a predetermined distance eachtime a switch is depressed.

In case of performing machining in a desired shape by the manual feed asdescribed above, since a conventional numerical control unit is notequipped with means for preventing excessive cutting, interference orthe like in the manual operation, it is necessary for an operator tomake machining by paying attention to the excessive cutting,interference or the like. In high-speed machining, since machining isperformed at high speed, it is particularly necessary to pay attentionto the excessive cutting, interference or the like. Thus, machiningtakes a long time and requires a skill, so that every operator could notperform machining manually with ease.

SUMMARY OF INVENTION

It is an object of the present invention to easily perform machining ina desired shape by the manual feed.

A method of specifying a machining limit area of the present inventioncomprises the steps of: defining a desired machining shape by shapingdata or a combination of the shaping data on an X-Y plane; andspecifying a machining limit area in which movement of the tool ispermitted in machining, based on the defined machining shape. Further, amanual feed machining method of the present invention utilizes themachining limit area specified by the above specifying method to performmachining by feeding a tool on condition that movement of the tool islimited within the machining limit area.

The machining limit area of the present invention means an area in whichthe movement of the tool is permitted in machining, and may be specifiedbased on a desired machining shape. The specified machining limit areamay include a machining limit area in an X- and/or a Y-axis directionand a machining limit area in a Z-axis direction.

In specifying the machining limit area on the X-Y plane, a desiredmachining shape is determined by shaping data or a combination of someshaping data on the X-Y plane at a predetermined Z-coordinate, and thedesired machining shape determined by the shaping data is specified as amachining limit area in which the tool can be moved on the X-Y plane inmanual machining using a numerical control unit. A circular-arc orstraight-line may be used as the shaping data to define the shape of themachining limit area.

In the case where the shape on the X-Y plane varies in a Z-axisdirection, the shaping data on the X-Y plane may be specified by meansof a function using a Z-coordinate value as a parameter. Thus, themachining limit area on the X-Y plane at different Z-coordinate valuescan be defined by specifying the machining limit area on the X-Y planeby the shaping data according to the above method, and varying theshaping data using the above function using the Z-coordinate value as aparameter. As the result, the shape initially specified on the X-Y planeat the predetermined coordinate position is reduced or enlarged in theZ-axis direction.

In specifying the machining limit area in the Z-axis direction, adesired machining shape is determined by shaping data or a combinationof some shaping data on the X-Y plane and a function using theZ-coordinate value as a parameter. Then, this function is converted intoan inverse function using an X- or a Y-coordinate value as a parameter,to obtain a function for specifying the Z-coordinate value of the toolwith respect to the coordinates of the machining limit area on the X-Yplane.

The specified machining limit area in the Z-axis direction may be set inaccordance with the depth of cut, i.e., the maximum depth of cut in theZ-axis direction in one cutting process of the tool. Thus, it ispossible to prevent the excessive cutting which may be caused by thealteration of the depth of cut.

Further, in a machining method using a numerical control unit of thepresent invention, machining is performed by manually feeding a tool inaccordance with the specified machining limit area, i.e., the machininglimit area in the X- and/or Y-axis direction and/or the machining limitarea in the Z-axis direction depending on a direction in which themachining limit area is to be specified.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an essential part of a numericalcontrol unit and a machine tool controlled by the numerical control unitfor carrying out a method of the present invention;

FIG. 2 is a perspective view showing a hemispherical convex machiningshape;

FIG. 3 is a schematic view showing a display screen for specifying amachining limit area based on the machining shape shown in FIG. 2;

FIG. 4 is a perspective view showing a convex machining shape defined bycircular-arc and straight-line portions;

FIG. 5 is a schematic view showing a display screen for specifying amachining limit area based on the machining shape shown in FIG. 5;

FIG. 6 is a perspective view showing a hemispherical concave machiningshape;

FIG. 7 is a schematic view showing a display screen for specifying amachining limit area based on the machining shape shown in FIG. 6;

FIG. 8 is a perspective view showing a machining shape defined bycircular-arc and straight-line portions;

FIG. 9 is a schematic view showing a display screen for specifying amachining limit area based on the machining shape shown in FIG. 8;

FIG. 10 is a perspective view showing a conical concave machining shape;

FIG. 11 is a schematic view showing a display screen for specifying amachining limit area based on the machining shape shown in FIG. 10;

FIG 12 is a flow chart showing the processing for machining in an X-axisdirection according to a machining method of the present invention;

FIG. 13 is a flow chart showing the processing for obtaining a limitvalue in an X-axis direction;

FIG. 14 is a flow chart showing the processing for machining in a Z-axisdirection according to the machining method of the present invention;

FIG. 15 is a flow chart showing the processing for renewing a machininglimit value; and

FIG. 16 is a flow chart showing the different processing for renewing amachining limit value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a description will be given on a numerical control unit 10 to beused for carrying out a method of the present invention and a machinetool controlled by the numerical control unit referring to FIG. 1.

In FIG. 1, a CPU 11 in a numerical control unit 10 reads out a systemprogram from a ROM 12 through a bus 16, and controls the whole numericalcontrol unit 10 according to the system program. A RAM 13 storestemporary calculation data, display data and various data inputted by anoperator through a CRT/MDI unit 20. A non-volatile memory 14 such as aCMOS memory is backed up by a battery (not shown) to retain storage dataeven if a power source of the numerical control unit 10 is turned off,and stores an NC machining program read through an interface (not shown)or the CRT/MDI unit 20, parameter values necessary for drive controllinga machine tool, etc. Further, various system programs for performing theprocessing in a data input mode necessary for creating and editing theNC machining program and in a playback mode for automatic operation arepreliminarily stored in the ROM 12. In addition, a program forperforming the processing of specifying a machining limit area accordingto the present invention is also stored in the ROM 12.

External devices such as a data input device and an external storagedevice are connected to an interface (not shown), so that the NCmachining program or the like is read through these external devices,and the NC machining program edited in the numerical control unit 10 canbe outputted from the numerical control unit 10 to the external devices.

A PC (Programmable Controller) 15 controls auxiliary devices of themachine tool, for instance, an actuator such as a robot hand forexchanging tools according to a sequence program stored in the numericalcontrol unit 10. Thus, the PC 15 performs conversion of signals for theauxiliary devices according to the sequence program and outputs theconverted signals to the auxiliary devices of the machine tool throughan input/output unit (not shown) in accordance with M function,S-function and T-function commanded by the NC machining program. Theauxiliary devices such as actuators are operated in response to theoutput signals. Further, the PC receives signals from limit switches ona body of the machine tool and the auxiliary devices, and also variousswitches on a control panel of the machine tool, to perform thenecessary processing on the signals and transfer the processed signalsto the CPU 11.

Image signals including a current position of each axis of the machinetool, an alarm and image data are sent to the CRT/MDI unit 20, and aredisplayed on a display device 22 through a graphic control circuit 21.The CRT/MDI unit 20 comprises a manual data input unit with the graphiccontrol circuit 21, the display device 22, a keyboard and varioussoftware keys 24, and transfers data to the CPU 11 through the bus 16.Further, a system program for manual programming stored in the ROM 12may be started to make the display device 22 display an interactiveframe so that input of data regarding a shape or the like is permittedfor creating a machining program and input of data in an interactivemanner. A manual pulse generator 52 can be provided on a control panelof the machine tool 50, for instance, and is used for preciouspositioning of movable parts of the machine tool by controlling eachaxis based on distributed pulses according to the manual operation.

An axis control circuit 30 receives a motion command for each axis fromthe CPU 11 and outputs a command for each axis to a servo amplifier 40.The servo amplifier 40 drives a motor for each axis in accordance withthe command. A pulse coder for position detection is built in the servomotor for each axis, and position signals are fed back as a pulse trainfrom the pulse coder. When occasion demands, a linear scale is used asthe position detector.

Similarly, with respect to a spindle (not shown) of the machine tool, aspindle control circuit receives a spindle rotation command and outputsa spindle speed signal to a spindle amplifier. The spindle amplifierreceives the spindle speed signal and rotates a spindle motor of themachine tool at the commanded speed. A position coder is connected tothe spindle motor, and outputs feedback pulses in synchronization withthe rotation of the spindle, and the feedback pulses are read by the CPU11. In addition, in case of positioning the spindle at a predeterminedangular position commanded by the machining program, the spindle isstopped and held at the predetermined angular position under positionalcontrol of the spindle, i.e., C-axis control by processing of the CPU 11using a one-rotation signal outputted from the position coder.

The non-volatile memory 14 may be utilized as a parameter memory forstoring the specified machining limit area. Further, the non-volatilememory 14 may store functions for defining the machining limit area.

A method of specifying a machining limit area for the numerical controlunit of the present invention will be described referring to FIGS. 2-11.FIGS. 2-5 show cases of specifying a machining limit area of a convexshape, and FIGS. 6-9 show cases of specifying a machining limit area ofa concave shape. Further, FIGS. 10 and 11 show a case of varying amachining limit area on an X-Y plane in accordance with the position ona Z-axis.

A first example is a case of specifying a convex machining limit area onthe basis of a hemisphere. As shown in FIG. 2, the hemisphere forspecifying a machining limit area has a circular cross section on an X-Yplane and a radius of a circle in the cross section gradually decreasesin a Z-axis direction. FIG. 3 shows an example of a displayed image inspecifying a machining limit area of a convex shape on the basis of thehemisphere shown in FIG. 2. On the display screen, the machining limitarea is specified by shaping data such as circular-arc or straight-linedata. In the displayed image shown in FIG. 3, the machining limit areais specified by determining a sectional shape on the X-Y plane and theX-Z or Y-Z plane.

Regarding the X-Y plane, the machining limit area on the X-Y plane isspecified by inputting circle data including a center position (X0, Y0)and a radius r at the predetermined Z-coordinate. On the other hand, thedisplayed image on the X-Z plane shows variation of the length of themachining limit area in the X-axis direction with respect to the Z-axisdirection by means of the sectional shape as viewed from the Y-axisdirection. The length in the X-axis direction with respect to the Z-axisdirection is defined by a function. For instance, this function may beexpressed by fx(Z) which is inputted through the input means such as thekeyboard 23 in the CRT/MDI unit 20 and stored in the non-volatile memory14.

The definition using the functions is used for varying the shape on theX-Y plane at the predetermined Z-coordinate with the Z-coordinate valueas a parameter. For instance, the X-Z plane in the display screen showsa variation of the length of the machining limit area in the X-axisdirection with respect to the Z-axis direction by means of the sectionalshape as viewed from the Y-axis direction, and the length in the X-axisdirection with respect to the Z-axis direction can be defined by fx(Z)so that the X-coordinate is determined by fx(Z). Further, the Y-Z planein the display screen shows a variation of the length of the machininglimit area in the Y-axis direction with respect to the Z-axis directionby means of the sectional shape as viewed from the X-axis direction, andthe length in the Y-axis direction with respect to the Z-axis directioncan be defined by fy(Z) so that the Y-coordinate is determined by fy(Z).The functions fx(Z) and fy(Z) may be inputted through the input meanssuch as the keyboard 23 in the CRT/MDI unit 20.

The functions fx(Z) and fy(Z) may be determined as follows. The functionA(Z) defines a sectional shape taken perpendicularly to the Y-axis at adesired point on the Y-axis passing through a center of the shape on theX-Y plane. The function fx(Z) may be determined by giving the coordinateof the desired point on the Y-axis for defining the sectional shape.When a desired point on the Y-axis for determining the function fx(Z) isnot given, the sectional shape is uniformly defined irrespectively ofthe position on the Y-axis. Similarly, the function fy(Z) defines asectional shape taken perpendicularly to the X-axis at a desired pointin the X-axis passing through the center of the shape on the X-Y plane.

Thus, the machining limit area of the convex shape can be specified suchthat the shape determined on the X-Y plane at a certain Z coordinate isvaried in accordance with the functions fx(Z) and fy(Z). In the casewhere a circle is inputted as shaping data on the X-Y plane, enlargementor reduction of a radius in the Z-axis direction may be specified byusing either of the functions fx(Z) and fy(Z).

The machining limit area in which a tool can be moved in the Z-axisdirection may be determined in accordance with a maximum depth of cut inthe Z-axis direction in one cutting process.

A slant-lined portion in FIG. 3 shows a portion in which the movement ofthe tool is inhibited. That is, the machining limit area is specified asa portion other than the slant-lined portion.

A second example is to specify a machining limit area of a convex shapeon the basis of a part of a pipe-like shape having a curved portion. Asshown in FIG. 4, the shape for specifying the machining limit area hasrectangular portions on the opposite ends of a circular-arc portion onthe X-Y plane, and a width is decreased in the Z-axis direction. FIG. 5shows a displayed image in specifying the machining limit area of theconvex shape on the basis of the machining shape shown in FIG. 4. On thedisplay screen, the machining limit area is specified on the basis ofshaping data such as circular-arc data or straight-line data. In thedisplayed image shown in FIG. 5, the machining limit area is specifiedby determining sectional shapes on the X-Y plane and the X-Z or Y-Zplane.

Regarding the X-Y plane, the machining limit area on the X-Y plane isspecified by inputting circular-arc data including a center position(X0, Y0), a radius and an open angle θ, etc. and straight-line data(including positions and lengths X1, Y1, etc.) for defining rectangleson the opposite ends of the circular-arc portion in the predeterminedZ-coordinate. On the other hand, on the X-Z plane, a variation of thelength of the machining limit area on the X-axis direction with respectto the Z-axis direction is shown by means of the sectional shape asviewed from the Y-axis direction. The length on the X-axis directionwith respect to the Z-axis direction can be specified by the functionfx(Z), similarly to the first example.

On the other hand, the machining limit area in the Z-axis direction maybe specified by using the functions in the same manner as in the firstexample. Thus, the machining limit area of the convex shape is specifiedsuch that the shape determined on the X-Y plane at a certainZ-coordinate is varied in accordance with the functions fx(Z) and fy(Z).Incidentally, a slant-lined portion in FIG. 5 shows a portion in whichthe movement of the tool is inhibited.

A third example is to specify a machining limit area of a concave shapeon the basis of a hemispherical machining shape. As shown in FIG. 6, aconcave hemisphere for specifying the machining limit area is formed bycircles formed in rectangles on the X-Y planes with their radiusdecreasing in the Z-axis direction. FIG. 7 shows an example of displayedimage in specifying the machining limit area of the concave shape on thebasis of the hemispherical machining shape shown in FIG. 6. On thedisplay screen, the machining limit area is specified by determining theshape of the rectangular portion using shaping data such asstraight-line data, and by determining the concave hemispherical portionusing circular-arc data. Further, in the displayed image shown in FIG.7, the machining limit area is specified by determining the sectionalshapes on the X-Y plane and the X-Z or Y-Z plane.

Regarding the X-Y plane, an outer machining limit area is specified byfour straight-line data in the predetermined Z-coordinate, while amachining limit area of the circular arc in the concave portion isspecified by circular-arc data including a center position (X0, Y0) anda radius r. On the other hand, the displayed image on the X-Z planeshows a variation of the length of the machining limit area in theX-axis direction with respect to the Z-axis direction by means of thesectional shape as viewed from the Y-axis direction, and may bespecified by the straight-line data and the circular-arc data or thefunction fx(Z). Similarly, the displayed image in the Y-Z plane shows avariation of the length of the machining limit area in the X-axisdirection to the Z-axis direction by means of the sectional shape asviewed from the X-axis direction, and may be specified by the straightline data and the circular-arc data or the function fy(Z).

The machining limit area in the Z-axis direction may be also specifiedby using the function, similarly to the first and second embodiments.Thus, the machining limit area of the concave shape can be specifiedsuch that the shape determined on the X-Y plane at a certainpredetermined Z-coordinate is varied in accordance with the functionsfx(Z) and fy(Z). Incidentally, a slant-lined portion in FIG. 7 shows aportion in which the movement of the tool is inhibited.

A fourth example is to specify a machining limit area of a concave shapeon the basis of a part of a pipe-like machining shape having a curvedportion. As shown in FIG. 8, the shape for specifying the machininglimit area has a concave portion in a rectangular parallelepiped and hasrectangles on the opposite ends of a circular-arc portion on the X-Yplane with its width decreasing in the Z-axis direction. FIG. 9 shows anexample of a displayed image in specifying the machining limit areahaving the concave portion on the basis of the machining shape shown inFIG. 7. On the display screen, the machining limit area is specified bydetermining the shape of the rectangular portion by shaping data such asstraight-line data, and by determining the shape of the concave portionby circular-arc data and straight-line data. Further, in the displayedimage shown in FIG. 9, the machining limit area is specified bydetermining the sectional shapes on the X-Y plane and the X-Z or Y-Zplane.

Regarding the X-Y plane, an outside machining limit area of therectangular shape is specified using four straight-line data in thepredetermined Z-coordinate, while the concave portion is specified usingthe circular-arc data including a center position (X0, Y0), radii R1, R2and an open angle θ and straight-line data inside the rectangularportion. On the other hand, the displayed image on the X-Z plane shows avariation of the length of the machining limit area in the X-axisdirection with respect to the Z-axis direction by means of the sectionalshape as viewed from the Y-axis direction, and may be specified by thestraight line data and the circular-arc data or the function fx(Z).Similarly, the displayed image on the Y-Z plane shows a variation of thelength of the machining limit area in the Y-axis direction with respectto the Z-axis direction by means of the sectional shape as viewed fromthe X-axis direction, and may be specified by the straight-line data andthe circular-arc data or the function fy(Z).

On the other hand, the machining limit area in the Z-axis direction maybe specified by using the function, similarly to the above first, secondand third example. Thus, the machining limit area of the concave shapemay be specified such that the shape determined on the X-Y plane in thecertain Z-coordinate varies in accordance with the functions fx(Z) andfy(Z). Incidentally, a slant-lined portion in FIG. 9 shows a portion inwhich the movement of the tool is inhibited.

A description will be made on the variation of the shape on the X-Yplane with respect to the Z-coordinate using the functions, referring toFIGS. 10 and 11. In this example, the description will be given on acase where a concave portion of a conical shape is specified as themachining limit area, as shown in FIG. 10.

With respect to the concave machining limit area of the conical shapeshown in FIG. 10, the shape on the X-Y plane in the predeterminedZ-coordinate can be specified by circle data shown in FIG. 11, similarlyto the above example, and a slant-lined portion shows a portion in whichthe movement of the tool is inhibited. In FIG. 11, the displayed imageon the X-Z or Y-Z plane shows a variation of the machining limit area inthe Z-axis direction. The following description is made with respect tothe X-Z plane. The displayed image on the X-Z plane shows a section asviewed from the Y-axis direction which indicates a boundary of themachining limit area in the X-axis direction with respect to the Z-axisdirection. In the example shown in FIG. 11, the boundary is defined by astraight line between (X1, Z1) and (0, Zn) and a straight line between(−X1, Z1) and (0, Zn). The boundary can be specified by shaping date ofstraight lines or circular arcs, or otherwise, by a function fx(Z) usingthe Z-coordinate value as a parameter, which represents the relationshipbetween the Z-coordinate and X-coordinate, if it is not specified by theabove shaping data.

In the case where the machining limit area is symmetrical about theZ-axis, the machining limit area can be specified by either the firstquadrant or the second quadrant.

The machining limit area may be also specified on the Y-Z plane by theprocess similar to that on the X-Z plane, and hence the descriptionthereof will be omitted.

Further, when the machining limit area is symmetrical about the Z-axis,it is possible to specify this machining limit area only by either ofthe X-Z plane and the Y-Z plane.

Accordingly, by determining the machining limit area on the X-Y plane ata certain predetermined Z-coordinate position and the function fx(Z) isdefined with respect to the machining limit area, the machining limitarea with respect to a position in the Z-axis can be specified. Forinstance, in the case where a machining limit area of a circle L1 on theX-Y plane at the Z-coordinate value of Z1 is specified and the functionx(Z) is defined with respect to the machining limit area, it is possibleto specify a machining limit area of a circle L2 on the X-Y plane at theZ-coordinate value of Z2, by obtaining a function value fx(Z2) of theZ-coordinate value of Z2.

In the example shown in FIG. 11, the function fx(Z) represents straightlines, however, an arbitrary function may be used for defining themachining limit area.

A description will be made on a machining method of performing machiningby manually feeding a tool using the specified machining limit area.Since machining by manual feed is performed with respect to every eachaxis of the X-, Y- and Z-axes, machining operation on every each axiswill be described. As machining in the X-axis direction is same as thatin the Y-axis direction, machining in the X-axis direction will be onlydescribed, referring to FIGS. 12 and 13, while a description ofmachining in the Y-axis direction will be omitted. Further, machining inthe Z-axis direction will be described referring to FIGS. 14 to 16.FIGS. 15 and 16 show machining with alteration of the machining limitarea in the Z-axis direction.

First, a description will be made on machining in the X-axis directionusing FIGS. 12 and 13. In machining in the X-axis direction,distribution pulses to be supplied to the axis control circuit 30 areobtained. The distribution pulses can be generated by driving the manualpulse generator 52. The numerical control unit 10 performs the axisdriving on the basis of the distribution pulse (Step S1).

The numerical control unit 10 reads a current position x of the toolstep S3), obtains a limit value XL in the X-axis direction through theprocessing in the following Steps S4 to S6, and compares the currentposition x with the limit value XL in the X-axis direction (Step S7).

When the current position x of the tool does not reach the limit valueXL in the X-axis direction, the pulse distribution is performed to movethe tool in the X-axis direction (Step S8). The tool is movedcontinuously until it is determined in the comparison processing in theStep S7 that the current position x of the tool reaches the limit valueXL in the X-axis direction, i.e., the tool reaches the machining limitarea, or the distribution pulses are finished in Step S2.

As to the limit value XL in the X-axis direction, it is determinedwhether or not the tool is moved in the Z-axis direction (Step S4), andwhen it is determined that the tool is moved in the Z-axis direction, anew limit value XL is obtained in Step S5. As shown in FIG. 13, in theprocessing of Step S5, a current position z of the tool in the Z-axisdirection is read (Step S10) and a new limit value XL in the X-axisdirection is obtained through arithmetic operation of substituting thecurrent position z for the parameter Z of the function A(Z) (Step S11).When it is determined that the tool is not moved in the Z-axisdirection, the previous limit value XL in the X-axis direction is used(Step S6). When distribution pulses are newly generated by furtherdriving the manual pulse generator 52, the above operation is repeatedlyperformed.

A description will be made on machining in the Z-axis direction usingFIG. 14. In machining in the Z-axis direction, distribution pulses to besupplied to the axis control circuit 30 are obtained by driving themanual pulse generator 52. The numerical control unit 10 performs theaxis driving on the basis of the distribution pulses (Step S20).

The numerical control unit 10 reads a current position z of the tool(Step S22), obtains a limit value ZL in the Z-axis direction through theprocessing of the following Steps S23 to S25, and compares the currentposition z with the limit value ZL in the Z-axis direction (Step S26).

When the current position z of the tool does not reach the limit valueZL in the Z-axis direction, the pulse distribution is performed to movethe tool in the Z-axis direction (Step S27). The tool is movedcontinuously until it is determined in the comparison processing in StepS24 that the current position z of the tool reaches the limit value ZLin the Z-axis direction, i.e., the tool reaches the machining limitarea, or the distribution pulses are finished in Step S21.

As to the limit value ZL in the Z-axis direction, it is determinedwhether or not the tool is moved in the X- or Y-axis direction (StepS23), and when it is determined that the tool is moved in the X- orY-axis direction, a new limited value ZL is obtained in Step S24. Asshown in FIG. 16, in the processing in Step 24, a current value X or Yof the X- or 20 Y-coordinate of the tool is obtained (Step S60), and aninverse function fx⁻¹(X) or fy⁻¹(Y) using X or Y as a parameter isobtained in advance based on the function f(Z) or fy(Z) with theZ-coordinate value as a parameter, and a new limit value ZL in theZ-axis direction is obtained by substituting the current position X or Yfor the inverse function (Step S61). When it is determined that the toolis not moved in the X- or Y-axis direction, the previous limit value ZLin the Z-axis direction is used (Step S25).

The limit value ZL in the Z-axis direction can be altered in the courseof machining in the Z-axis direction. An example of renewing the limitvalue will be described referring to FIG. 15. In FIG. 15, a currentposition Z of the tool is set as the limit value ZL in the Z-axisdirection. The renewal is performed by depressing a renewal button orthe like, when an operator has manually moved the tool by a cuttingdepth in the Z-axis direction and desires to set the current position ofthe tool as the limit value ZL.

When the distribution pulses are newly generated by further driving themanual pulse generator 52, the above operation is repeatedly performed.

As has been described heretofore, according to the present invention,machining of a desired shape by the manual feed operation can beperformed easily using the numerical control unit.

What is claimed is:
 1. A method of specifying a machining limit area inmachining a workpiece by manually feeding a tool relative to theworkpiece using a numerical control unit, comprising: defining a desiredmachining shape by shaping data or a combination of the shaping data onan X-Y plane; and specifying a machining limit area in which movement ofthe tool is permitted in machining, based on the machining shape definedin said defining, wherein said defining includes specifying said shapingdata on the X-Y plane by a function using a Z-coordinate value as aparameter, and the machining limit area on the X-Y plane in saiddefining is variable in accordance with said function.
 2. A method ofspecifying a machining limit area according to claim 1, wherein saiddefining includes converting said function into an inverse functionusing an X- or Y-coordinate value as a parameter, and specifying themachining limit area in which movement of the tool is permitted in theZ-axis direction, based on said inverse function.
 3. The method ofspecifying a machining limit area according to claim 1, wherein saiddefining includes defining said machining shape by a circular-arc and/ora straight line.
 4. A method of specifying a machining limit area inmachining a workpiece by manually feeding a tool relative to theworkpiece using a numerical control unit, comprising: defining a desiredmachining shape by shaping data or a combination of the shaping data onan X-Y plane; and specifying a machining limit area in which movement ofthe tool is permitted in machining, based on the machining shape definedin said defining, wherein said specifying further includes setting amachining limit area in which movement of the tool is permitted in theZ-axis direction in accordance with the maximum depth of cut in theZ-axis direction in one cutting process.
 5. The method of specifying amachining limit area according to claim 4, wherein said definingincludes defining said machining shape by a circular-arc and/or astraight line.
 6. A method of machining a workpiece by manually feedinga tool relative to the workpiece using a numerical control unit,comprising: defining a desired machining shape by shaping data on an X-Yplane; specifying a machining limit area in which movement of the toolis permitted in machining, based on the machining shape defined in saiddefining; and performing machining by feeding the tool on condition thatthe movement of the tool is limited within said machining limit area,wherein said defining includes specifying said shaping data on the X-Yplane by a function using a Z-coordinate value as a parameter, and themachining limit area on the X-Y plane in said defining is variable inaccordance with said function.
 7. The method of specifying a machininglimit area according to claim 6, wherein said defining includes definingsaid machining shape by a circular-arc and/or a straight line.
 8. Amethod of machining a workpiece by manually feeding a tool relative tothe workpiece using a numerical control unit, comprising: defining adesired machining shape by shaping data on an X-Y plane; specifying amachining limit area in the X- and/or Y-axis direction in which movementof the tool is permitted in machining, based on the machining shapedefined in said defining; specifying a machining limit area in whichmovement of the tool is permitted in a Z-axis direction; performingmachining on the X-Y plane by feeding the tool on condition that themovement of the tool is limited within said machining limit area in theX- and/or Y-axis direction; and performing machining in the Z-axisdirection by feeding the tool on condition that the movement of the toolis limited within said machining limit area in the Z-axis direction,wherein said defining includes specifying said shaping data on the X-Yplane by a function using a Z-coordinate value as a parameter, and themachining limit area on the X-Y plane in said defining is variable inaccordance with said function.
 9. The method of specifying a machininglimit area according to claim 8, wherein said defining includes definingsaid machining shape by a circular-arc and/or a straight line.
 10. Acomputer readable storage medium, storing a computer program instructinga computer to perform: defining a desired three-dimensional machiningshape by shaping data on an X-Y-Z plane; and specifying a machininglimit area in which movement of a tool is permitted in machining, basedon the machining shape defined in said defining, wherein said definingincludes specifying said shaping data on the X-Y plane by a functionusing a Z-coordinate value as a parameter, and the machining limit areaon the X-Y plane in said defining is variable in accordance with saidfunction.
 11. The computer readable storage medium recited in claim 10,wherein said defining includes converting said function into an inversefunction using an X- or Y-coordinate value as a parameter, andspecifying the machining limit area in which movement of the tool ispermitted in the Z-axis direction, based on said inverse function. 12.The computer readable storage medium according to claim 10, wherein saiddefining includes defining said machining shape by a circular-arc and/ora straight line.
 13. A computer readable storage medium, storing acomputer program instructing a computer to perform: defining a desiredthree-dimensional machining shape by shaping data on an X-Y-Z plane; andspecifying a machining limit area in which movement of a tool ispermitted in machining, based on the machining shape defined in saiddefining, wherein said specifying further includes setting a machininglimit area in which movement of the tool is permitted in the Z-axisdirection in accordance with the maximum depth of cut in the Z-axisdirection in one cutting process.
 14. The computer readable storagemedium according to claim 13, wherein said defining includes definingsaid machining shape by a circular-arc and/or a straight line.
 15. Anapparatus comprising: a defining unit defining a desiredthree-dimensional machining shape by shaping data on an X-Y-Z plane; anda prohibition unit prohibiting movement of a tool in a limit area basedon the machining shape defined in said defining, wherein said definingunit specifies said shaping data on the X-Y plane by a function using aZ-coordinate value as a parameter, and the machining limit area on theX-Y plane in said defining is variable in accordance with said function.16. The apparatus recited in claim 15, wherein said defining unitconverts said function into an inverse function using an X- orY-coordinate value as a parameter, and specifying the machining limitarea in which movement of the tool is permitted in the Z-axis direction,based on said inverse function.
 17. The apparatus according to claim 15,wherein said defining includes defining said machining shape by acircular-arc and/or a straight line.
 18. An apparatus comprising: adefining unit defining a desired three-dimensional machining shape byshaping data on an X-Y-Z plane; and a prohibition unit prohibitingmovement of a tool in a limit area based on the machining shape definedin said defining, wherein said specifying unit sets a machining limitarea in which movement of the tool is permitted in the Z-axis directionin accordance with the maximum depth of cut in the Z-axis direction inone cutting process.
 19. The apparatus according to claim 18, whereinsaid defining includes defining said machining shape by a circular-arcand/or a straight line.